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SURVIVAL STRATEGY. “The pervasive horizontal transfer of cif genes may allow them to evade inevitable extinction within symbiont lineages by escaping into a new symbiont population. This process is analogous to the evolution of transposable elements, which frequently go extinct within host species, but persist long term by jumping into new species.” https://lnkd.in/dXjWp9f View in LinkedIn

CROSSING SPECIES BARRIER. “Consistent with this process of clade selection, Wolbachia frequently jumps between host species. Our observations suggest that clade selection may also be acting at the level of the cif genes as Wolbachia genomes appear to be frequently recolonized by cif genes from other symbionts.” https://lnkd.in/dXjWp9f View in LinkedIn

HORIZONTAL TRANSFER. “The frequent loss of cif genes raises a paradox when trying to explain the high prevalence of CI across Wolbachia strains. Hurst and McVean (1996) argued that CI-inducing Wolbachia infections were more likely to transfer horizontally between host species, so symbiont strains that induce CI are more likely to persist over an evolutionary timescale.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

REMAINING QUESTIONS. “In particular, the identification of the insect factors targeted by the sperm modification may soon allow us to study the coevolution of cif genes with the insect reproductive system. Finally, a deeper analysis of divergent cif homologs found outside Wolbachia should allow us to address questions around the deep evolutionary origin of CI and may reveal novel functions of these genes.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

OPEN ISSUE. “Therefore, it remains to be demonstrated whether the degeneration of cif genes causes the loss of Wolbachia from populations.” https://lnkd.in/dXjWp9f View in LinkedIn

CONCLUSION. “Our study illustrates the dynamic evolution of CI genes and highlights the high rates of gene loss and horizontal gene transfer. Further functional analysis will open new avenues of research and allow us to reconstruct the full evolutionary history of CI.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

POSITIVE SYMBIOSIS. “Since the publication of theoretical studies on CI evolution, it has become increasingly clear that many Wolbachia strains can persist in host populations without inducing any reproductive manipulation by providing fitness benefits.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

TESTS FOR THE HYPOTHESIS. “It would be interesting to test whether these domains allow manipulation of reproduction across a broader host range. Interestingly, one of these domains, the ovarian tumor domain (OTU), is also found in a toxin involved in male-killing induced by the symbiont Spiroplasma poulsonii, raising the possibility that some domains could be involved in multiple forms of reproductive manipulations.” https://lnkd.in/dXjWp9f View in LinkedIn

LOSS OF FUNCTION GENES. “Firstly, these mutations tend to be on terminal branches of the gene tree. Secondly, pseudogenes rarely accumulate many loss-of-function mutations. Although this suggests that cifA and cifB pseudogenes rarely codiverge with the Wolbachia genome for long periods, it is unclear whether this results from the loss of the Wolbachia infection or through the genes being deleted from the genome, for instance, by phage excision.” https://lnkd.in/dXjWp9f View in LinkedIn

HOMOLOGY. “Given the relative homogeneity of cifA domains and the similarities of these additional cifB domains with known toxins and eukaryotic-like ankyrin proteins, it is tempting to hypothesize that they are linked to the modification function by interacting with the host rather than the binding to cifA.” https://lnkd.in/dXjWp9f View in LinkedIn